Broadband wireless access systems typically support an idle-mode to minimize the power consumption of a mobile subscriber station (MSS). During the idle-mode, the MSS does not perform a handover procedure when moving between base stations in the same paging zone. Therefore, the MSS does not need to transmit uplink information for the handover procedure, which reduces corresponding power consumption.
A paging zone is defined as a zone that is controlled by a plurality of base stations called a paging group. Each of the base stations in the paging group has the same paging cycle (Paging_Cycle) and the same paging offset (Paging_Offset).
The MSS may make a request to a base station to switch to the idle-mode. The base station then provides a paging message including its paging-group ID, a corresponding paging cycle, and a corresponding paging offset. The corresponding MSS may thus be switched to the idle-mode. During the idle-mode, the MSS may determine whether to continue or terminate the idle-mode based on the paging message provided by the base station at each paging cycle.
If traffic needs to be transmitted by the MSS while in the idle-mode, the MSS may terminate the idle-mode. For example, the MSS may be enabled to terminate the idle-mode by the BS. Furthermore, if the MSS moves to another paging zone or loses its sync while in an idle-mode and is unable to receive a paging at a predefined time, the MSS may terminate the idle-mode.
When the MSS is in the idle-mode, the MSS normally receives a periodic paging to secure its free move in the same paging zone without performing the handover procedure.
In configuring a paging zone, a backbone message (paging-group-action), is transferred by wire between base stations. An exemplary paging-group-action backbone message is shown in Table 1.
TABLE 1FieldSizeNotes Message Type 8 bits Sender BS ID48 bitsBase station unique identifier (Samenumber as that broadcastedon the DL-MAP message)  Target BS ID48 bitsBase station unique identifier (Samenumber as that broadcastedon the DL-MAP message)   Time Stamp32 bitsNumber of milliseconds since midnightGMT (set to 0xTTTTTTT to ignore)   Action 4 bits0 - Assign target BS to paging groups1 - Remove target BS from paging groups2 - Query (which paging groups target BSbelong to?)3 - Information (Paging groups sender BDbelongs to)  Num Records 4 bitsNumber of paging-group-ID records  For(j=0; j<Num  Records; j++) { Paging-group_ID16 bitsPaging group IDPAGING_CYCLE16 bitsCycle in which the paging message istransmitted within the paging groupPAGING OFFSET 8 bitsMSS PAGING OFFSET parameter     } Security fieldTBDA means to authenticate this message  CRC field32 bitsIEEE CRC-32
The paging-group-action backbone message is communicated between base stations. The paging-group-action backbone message may be used for four purposes based on contents of an action field (Action). A receiving base station (target BS) may be assigned (designated) to a specific paging group (Action=0). Alternatively, the target BS may be excluded from the specific paging group (Action=1). Alternatively, the target BS may be queried regarding the paging group to which the target BS belongs (Action=2). Alternatively, the target BS may be informed of the paging group to which a transmitting base station (sender BS) belongs (Action=3).
Since a single base station may belong to one or more paging zones, the paging-group-action backbone message may contain information pertaining to a multitude of paging groups. The base stations may be informed of the paging cycle and offset used in each paging zone via the paging-group-action backbone message. Furthermore, the base stations may be dynamically assigned to the paging groups via the paging-group-action backbone message.
In switching an MSS to an idle mode, a DREG_REQ message (one of previous MAC messages) is used. A format of the DREG_REQ message is shown in Table 2.
TABLE 2SyntaxSizeNotesDREG-REQ_Message_Format( ) {Management Message 8 bitsType = 29De-registration Request 8 bits0x00 = SS de-registrationCoderequest from BSand network0x01 = request for MSSderegistration from ServingBS and invitation of MSSpagingAvailability mode0x02-0xFF = reservedPaging Cycle request16 bitsOnly valid if De-registrationRequest Code = 0x01TLV encoded parametersVariable}
An MSS may send a request to a serving base station that the MSS will be switched to idle mode by setting a De-registration Request Code of the DREG_REQ message to 0x01 and then delivering the DREG_REQ message to the base station. This enables delivery of a specific paging cycle.
The serving base station receives the DREG_REQ message and may respond to the request by the MSS via a conventional DREG_CMD message. A format of the DREG_CMD message is shown in Table 3.
TABLE 3SyntaxSizeNotesDREG-CMD_Message_Format( ) {Management Message Type = 298 bitsAction code8 bitsTLV encoded parametersVariable}
The serving base station may allow the switching to the idle mode via an action code (Action code=0x05). Alternatively, the serving base station may allow the MSS to make the request for the switching to the idle mode after a time duration (Action code=0x06). Alternatively, the serving base station may not allow the MSS to make the request for the switching to the idle mode until the serving base station transmits the DREG_CMD message (Action code=0x07).
Details of the action code of the DREG_CMD message are shown in Table 4.)
TABLE 4ActionCodeAction0x00SS shall leave the current channel and attempt to access another channel0x01SS shall listen to the current channel but shall not transmit until anRES_CMD message or DREG_CMD with Action Code 0x00 isreceived.0x02SS shall listen to the current channel but only transmit on the Basic,Primary Management, and Secondary Management Connections.0x03SS shall return to normal operations and may transmit on any of itsactive connections.0x04SS shall terminate current Normal Operations with the BS: the BS shalltransmit this action code only in response to any SS DREG_REQ.0x05Require MSS de-registration from Serving BS and request initiation ofMSS idle mode.0x06The MSS may retransmit the DREG_REQ message after the timeduration (REQ-duration) given by.0x07The MSS shall not retransmit the DREG_REQ message and shall wait theDREG-CMD message.0x08-0xFFReserved
Base stations belonging to the same paging zone may be able to share the information pertaining to the MSS switched to the idle mode. Using this information, the serving BS may notify the MSS of procedures to execute in each paging cycle.
A Paging-announce backbone message is shown in Table 5.
TABLE 5FieldSizeNotes  Message Type 8 bits  Sender BS ID48 bitsBase station unique identifier (Samenumber as that broadcastedon the DL-MAP message)   Target BS ID48 bitsSet to 0xffffff to ignore    Time Stamp32 bitsNumber of milliseconds since midnightGMT (set to 0xffffffffto ignore)   Num MSS 8 bitsNumber of MSSs to pageFor(j=0; j<Num MSS;    j++) { MSS MAC address48 bits PAGING_CYCLE16 bitsMSS PAGING CYCLE parameter PAGING OFFSET 8 bitsMSS PAGING OFFSET parameter    }  Security fieldTBDA means to authenticate this message   CRC field32 bitsIEEE CRC-32
The paging-announce backbone message may be delivered to all base stations belonging to the same paging zone. The base stations receiving the paging-announce backbone message perform the paging by matching MAC addresses of MSSs included in the message with the paging cycle and offset within the message.
Consequently, due to the paging-announce backbone message, all of the base stations belonging to a specific paging zone may identically maintain MAC addresses of MSSs to page. Thus, a specific MSS may receive its paging information at each paging cycle unless the MSS leaves (deviates from) a current paging zone.
A format of a paging message MOB-PAG_ADV transmitted to MSSs in the idle mode via paging by each base station is shown in Table 6. The paging message is delivered to MSSs in a broadcast format.
TABLE 6FieldSizeNotes    MOB_PAG- ADV_Message_Format( ) {Management Message Type=?? 8 bits Num_Paging Group IDs 8 bitsNumber of Paging Group Idsin this message     For(i=0;i<Num_Paging_Group_IDs; I)      {  Paging Group ID 8 bits      }For(j=0; j<Num _MACs; j++)Number of MSS MAC      {Addresses in message maybe determined from the lengthof the message (found inthe generic MACheader). MSS MAC address hash24 bitsThe hash is obtained bycomputing a CRC24 onthe MSS 48-bit MACaddress.The polynomial for thecalculation is 0x864CFB.    Action Code 2 bitsPaging action instruction toMSS00 = No Action Required01 = Perform Ranging toestablish locationand acknowledge message10 = Enter Network11 = Reserved      Reserved 6 bits      }}
The MSS receives the paging message and may decide whether to maintain the idle mode continuously (Action Code=00), whether to perform ranging to establish a location information update (Action Code=01), and/or whether to terminate the idle mode to receive downlink traffic (Action Code=10).
The MSS may terminate the idle mode if the MSS needs to transmit traffic (uplink traffic occurrence). The MSS also may terminate the idle mode if the MSS needs to receive traffic (downlink traffic occurrence). The MSS also may terminate the idle mode if the MSS is unable to receive a periodic paging due to deviation from a current paging zone or due to a transmission problem.
FIG. 1 is a diagram illustrating a procedure for terminating an idle mode of a mobile subscriber station (MSS) in case of downlink traffic occurrence.
Referring to FIG. 1, a procedure for terminating the idle mode in a MSS is explained, with respect to a case where downlink traffic 101 needs to be delivered to an MSS in an idle mode. Base stations are unaware of the domain to which the MSS in an idle mode belongs. Downlink traffic is unconditionally delivered to a first base station (initial base station) to which the MSS initially made the request for switching to the idle mode.
Upon receipt of the downlink traffic to the MSS, the initial base station sets an action code to 11 for all base stations lying within the paging zone of the initial base station. The initial base station then transmits a paging-announce backbone message to the MSS (S11).
Each of the base stations receive the paging-announce message, sets an action code of a paging message MOV_PAG_ADV to 10, and transmits the paging message all of the MSSs lying within the paging zone, in a broadcast format (S12).
The corresponding MSS receives the paging message, terminates the idle mode, and requests a second base station (current base station) that is in charge of the paging zone where the MSS currently lies, for a re-registration to a network (S13). The second base station receives a base station ID of the first base station via the paging-announce message.
The second base station receives the re-registration request and sets an action flag of an MSS_Info_Request backbone message to 1. The MSS_Info_Request backbone message is communicated between base stations by wire, and then transmitted to notify the first base station that the MSS is seeking to exit the paging zone (S14).
A format of an MSS_Info_Request backbone message is shown in Table 7.
TABLE 7FieldSizeNotesGlobal Header152 bitsFor (j=0; j<NumRecords; j++){MSS unique 48 bits48-bit unique identifier used by MSS (asidentifierprovided by the MSS or by theI-am-host-of message)Action flag 8 bits0 - Request information1 - MSS arrived from Idle mode2 - MSS has transitioned to another paginggroup}Security fieldTBDA means to authenticate this message
The first base station receives the MSS_Info_Request and notifies the base stations within the same paging zone that the MSS has terminated the idle mode and is to be deleted from a paging list.